This apparatus relates to computer numerically controlled (CNC) machine tools such as an edge grinding apparatus. More specifically, the invention relates to a CNC apparatus which uses a sensor such as a laser for processing blanks such as a glass sheet.
Machine tools such as an edge grinding apparatus include at least one grinding wheel, at least one rotatable holder for a blank, and at least one CNC device for controlling the grinding of the blank according to selected specification. The CNC machine tool may include a multi-axis, linear (X, Y axis) holder instead of a rotatable holder. In either case, a cutting tool moves relative to the blank or workpiece under the control of a programmable controller, including a computer program.
In a standard CNC glass grinding machine, an operator must adjust the CNC parameters to allow the CNC machine to grind the part where it is located on the machine. This can be a slow process and is difficult for many operators to master. The prior art process requires the operator to grind a part, check the part for even grind then adjust the X, Y and rotation offset parameters on the CNC control to move the CNC program to match the part location.
U.S. Pat. No. 5,588,899 discloses one solution to this problem. The apparatus of this patent is an opto-electronic device for positioning eye glass or spectacle lenses in a CNC grinding device. The opto-electronic detecting device includes a CCD (charge coupled device) camera, a first control unit that includes an electronic picture processing and evaluating system cooperating with a second control unit. The system requires the manufacturer of the lens blank to mark each blank. If the blanks are not pre-marked, a separate marking is necessary.
U.S. Pat. No. 5,956,253 discloses a more recent development which uses a video controlled CNC apparatus for processing blanks such as a glass sheet. The device uses a video camera and monitor to program the path of the grinding wheel. The system requires a CNC machine, video camera, a video monitor, a vision board and software to calculate the offset parameters.
The device of this invention uses a high accuracy sensor to locate and program the path of the grinding wheel rather than position the blank in the CNC grinding device. No pre-marking or separate processing steps are needed. The system requires a CNC machine, a high accuracy reflective sensor and software to calculate the offset parameters. An operator must initiate a load cycle. Once the part is loaded on the CNC machine, the operator must start the measurement cycle. The measurement cycle will move a sensor such as a laser along the program path, stop at each of the checkpoints, and find the edge of the glass. The system software will store the edge of the glass and report the position to the CNC control. The control will continue this cycle through all the checkpoints. When the part path is complete the control will calculate the required offsets. Thereafter, the system will process additional blanks automatically without repeated adjustments for each blank.
The sensor may be a through beam or reflective type beam. It also could be inferred, ultrasonic or laser beam. Reflective lasers may be the best choice because they have a very small beam diameter, not easily affected by water or dirt, reasonable cost, and can see most materials well. The laser does not require the software power of the camera system. Also, the laser operates with or without hard stops. The laser is especially useful with many different sized parts, irregular edges or spacially curved edges (rear view mirror). The glass or blank acts as a reflective surface for the laser.